16Hit1600
Advanced MathEasy–MediumSimplifying a product plus a constant

Advanced Math practice question

Which expression is equivalent to (x + 6)(x − 6) + 36?

  1. A. Correct
  2. B. x² + 72
  3. C. x² + 12x
  4. D. x² − 72

Answer: A. x²

(x + 6)(x − 6) = x² − 36, and adding 36 leaves x².

Why the other answers are wrong

B. x² + 72
x² + 72 adds 36 to x² + 36 (wrong sign on the product's constant).
C. x² + 12x
x² + 12x keeps a middle term; the cross terms cancel in (x + 6)(x − 6).
D. x² − 72
x² − 72 subtracts 36 instead of adding.

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